When pollen lands on stigma, pollen tube grows down the style and into the ovary of the pistil.
Pollen tube formation is assisted by sugary solution, Calcium and Boron present provided by Stigma. The tube nucleus followed by two male gametes can enter the embryo sac in one of the three ways:
1. In Porogamy, entry is via Micropyle, which is most common.
2. Mesogamy allows entry through the integuments or funicle. It is seed in Cucurbita.
3. In Chalazogamy, entry is through the chalaza. It is seen in Casuarina.
Filiform apparatus helps in the guiding the pollen tube to egg cell. The tip of the pollen degenerates and the two male gametes are released inside the embryo sac. The tube nucleus degenerates.